Japanese Pat. No. 43-22339 discloses extruding at low spinning speeds various polymers through combined orifices. Each combined orifice includes a large diameter central capillary and two or more smaller diameter satellite capillaries. The lengths of the various capillaries are not specified. The spun yarns are drawn under unspecified conditions yielding yarns composed of drawn filaments having cross-sectional shapes which vary continuously and cyclically along the length of each filament. When attempts were made to duplicate the teachings of this reference with polyester polymer, yarn drawn at normal draw ratios and then heated while relaxed exhibited only a small amount of crimp. When the draw ratio was reduced experimentally to an unusual ratio, the crimp level in the relaxed yarn increased to a marginally useful level. But fabrics made from either of these yarns have a harsh hand.
Japanese Patent Publication No. 42,415/1979 (which corresponds to U.S. patent application Ser. No. 825,495, filed Aug. 17, 1977) discloses spinning two polyester streams through a spinneret with converging capillaries. One of the streams has a higher speed than the other. The streams intersect in mid-air below the spinneret and upon attenuation, form a combined stream. An oscillation occurs in the combined molten stream such that the combined stream, when quenched into a filament, exhibits thick and thin regions along its length. When a number of these filaments are combined into a yarn and relaxed, a highly useful degree of crimp is obtained. Crimp development was said to be based on formation of alternating S-twist and Z-twisted helically coiled sections, i.e., in the manner of classical false twist texture. Fabrics made from the yarn typically have a soft, luxuriant hand. But, reproducibly manufacturing the spinnerets with converging capillaries is quite difficult leading to non-uniformity of yarns. There is a continuing need for self crimping yarns similar in nature to those described in Japanese Patent Publication No. 42,415/1979, which can be made in a more reproducible manner.
Applicant undertook research to explore basic aspects of the fibers and yarns described in Japanese Patent Publication No. 42,415/1979. It was found that filament structure and the mechanism of crimp development were different than previously believed. Briefly, it was found that the thick and thin sections in the filaments shrink, upon thermal treatment, in varying amounts. The thick sections shrink more than the thin sections. Yarns composed of these filament crimp upon thermal treatment because the greater shrinkage portions of filaments causes buckling of neighboring low shrinkage portions of filaments. The instant invention stems from this discovery.
In the invention, difficulties of the prior art processes are reduced or avoided and latently crimpable yarns having improved properties are provided.